The range of different vehicles used by the police force usually is quite varied for reasons you can only guess. Our county has gone from Caprices, Impalas, Ford Taurus, Chevy Luminas to Jeep Cherokees to Ford Crown Vics, and they had a 93 Mustang for awhile too. All of these vehicles are esentially the same as for their utility/speed/effectiveness except for the Jeep, which has 4x4 capability and is MUCH slower than the Intrepids etc and is usually used for the drug taskforce and the K-9 units.
I think the po-po probably shops for their vehicles based on price. The price on the Crown Vic went up in 98 when they changed the bodystyle and added hp, so they changed the vehicles they used to Chevy Impalas. Dodge intrepids recently went down in price, a year or so after the new style came out so they all use Intrepids now (here anyway).
I've only seen highway patrol units use Camaros, and that was near Springfield, Il.
As for weird cop cars, on a Ponitac Fiero website I saw a Fiero cop car... Hella gay idea if you ask me.